1. Field of the Invention
The present invention relates to a wet station apparatus used for cleaning or etching a semiconductor wafer, and more particularly, to a wet station apparatus having a quartz heater monitoring system and a method of monitoring thereof.
2. Background of the Related Art
In order to clean or wet etch a semiconductor wafer, a chemical solution contained in a chemical bath of the wet station apparatus needs to be preheated to an appropriate temperature. Presently, a heating element is used for heating the chemical bath. However, if the heating element directly contacts the chemical solution, it is likely to be eroded and damaged by the chemical solution. Also, the chemical solution can be contaminated by undesired impurities existing on the surface of the heating element. Accordingly, to prevent these problems, the heating element is put into a sealed quartz tube. This type of heating unit is called a quartz heater.
FIG. 1 is a schematic view illustrating a conventional wet station apparatus. The conventional apparatus, as shown in FIG. 1, includes: a chemical solution 10 which is used for cleaning or wet etching is semiconductor wafer, a chemical container 20 for holding the chemical solution 10, a temperature measuring device 30 for measuring the temperature of the chemical solution 10, a temperature control unit 40 for comparing a temperature measured by the temperature measuring device 30 with a predetermined reference temperature value and outputting the result thereof as a control signal N1, a quartz heater 50 for heating the chemical solution 10, a power supply controller 60 for receiving the control signal N1 and adjusting the power supplied to the quartz heater 50, a power switch 70 connected to the power supply controller 60 for switching power to the quartz heater 50, a Teflon coverlet 80 on which a wafer cassette is placed so as to prevent the quartz heater from directly contacting the wafer cassette during a cleaning or etching process, and a power connector 90 for connecting the quartz heater 50 with the power supply controller 60 and power switch 70.
Here, since the quartz heater 50 is located in the chemical solution 10, a conventional wet station apparatus generates the following problems.
First, if the quartz heater 50 is exposed to the chemical solution 10 for a long time, the quartz tube of the quartz heater 50 reacts with the chemical solution 10. Accordingly, pinholes are apt to form on the surface of the quartz tube or the quartz tube becomes very fragile. Thus, the heating element in the quartz tube 50 is easily eroded by exposure to the chemical solution 10, and the chemical solution 10 is contaminated by undesired impurities from the heating element.
Also, since the Teflon coverlet 80 covers the quartz heater 50, it is difficult to detect the damage of the quartz tube by visual inspection. Furthermore, a conventional wet station apparatus has no way of automatically detecting a damaged quartz tube, which results in severe accidents occurring during the process.
Second, in case where several quartz heaters are provided, even though a heating element of one quartz heater among them is eroded by the chemical solution and then disconnected, the process is continued with the remaining quartz heaters. Accordingly, the preheating time is increased, whereby processing time is also increased.
Third, in case that the power supply controller 60 malfunctions, because the conventional apparatus has no way of promptly detecting the problem, a warning signal is not generated until the quartz heater 50 has overheated.
As described above, because the conventional wet station apparatus, used for the cleaning and wet etching operations related to a semiconductor wafer, has no way of promptly detecting the damage to the quartz tube of the quartz heater nor the disorders of the power supply controller, severe accidents can occur during the process.